Civic D15B(Exi) Idle issue

[hammi]

Hi,
I just bought a Honda Accord 1987 it has Honda civic Exi Engine in it. The block code is D15B the Head code is P2A-5 Ecu is PEJ-J01.
The car has some weird idle issue. The idle usually stays above 1000rpm on idle. The IAC is working I can observe while turning on the AC or moving the steering. I have tried cleaning the throttle body and changing the complete throttle body too but no luck. Now after some lethal tries from the electricians the choke does not work at all on cold start and the car stalls when the gauge goes a little higher from C mark the choke starts working and Rpm goes to 1300-1400.

1. Car has thermostat valve and fans are automatic.
2. I disconnected the IAC while car running and BISS screw was fully tightened but the RPM was still at 1000.
3. There is no Air leak Car stalls if throttle is blocked.

[Hassan1991]

That's a weird combo.
Did you time the distributor right?

[hammi]

Not really how to do that? Got the distributor O Ring replaced but the issue existed before it.

[Hassan1991]

You need timing light gun for that.
If your car stays alive without iacv it means either iacv is stuck open or throttle body coin is not fully closed.

[hammi]

Throttle coin is fully closed. The TB is sucking air through the IAC port. If I close IAC air port opening the Engine almost stalls. If I remove the IAC and close the magnetic valve with my hand the car almost stalls. Is the magnetic Valve stuck?

[Hassan1991]

Yes iacv is not working. And it means there is no leak. Iac is causing change in rpm.
Have you test the wiring?
First check the wiring. Then check the iacv. Can be getting stuck or bad enough not to operate.

[hammi]

I got the wiring checked its all good. So if I remove the IAC the rpm should lower? I mean which way does it work. The IAC works as to open the valve or the valve is fully open and it closes it to restrict high air flow?

[Hassan1991]

it can be either a solenoid (2 wire) or stepper motor(3 wire) controlled by ecu.
consider throttle body stays close means no air will pass at idle from coin. Ecu will use Iacv to leak then air and thus control the rpm, it rise and lower the rpm, by controlling the amount of air passing through. more air means high rpm. on electric load or cold start ecu operated Iacv to control rpm.

[hammi]

Okay. What is the purpose of the two water pipes connected to it?

[Hassan1991]

Those are old iacv which also have coolant likes for warm idle settings.

[hammi]

Okay so if I disconnect the pipes it should have no affect on the rpm?

[Hassan1991]

With no coolant connection. Rpm will not get adjust with temperature of engine.

[hammi]

Does the coolant keeps the temp of the TB constant or does it also works as a thermostat to adjust the opening and closing of the TB depending on the water temperature?

[Hassan1991]

Not TB. It's for iacv. New engines iacv are totally controlled by ecu. In these old engines coolant lines are connected with iacv. Coolant allow iacv to close (to a certain limit) at optimum temperature.

[hammi]

So there is a chance that this mechanical part of the IACV controlled by water is not functioning right.
If the car is fully warmed up, BISS is fully tightened and IACV(electric) is disconnected the car should almost stall right? Or the Rpm should be below 700

[hammi]

Can you please tag Xulfiqar on this post. I dont know how to tag someone on a post.

[hammi]

Also Can a sticking thermostat be the culprit? Maybe its not allowing proper flow of the water through the TB which is causing it to stay open. Car takes a bit more time to reach normal operating temp compared to other cars so just a random thought lol

[Hassan1991]

@Xulfiqar

[Hassan1991]

Yes there can be a chance. You have to set Biss to original position. Not need to mess with it.
If thermostat valve is the problem it would have caused car to overheat
Check the iacv first.

[Xulfiqar]

The old d series engines have a small thermostat in the iacv too, thats what majorly controls the cold start idle rpm, it must be rusted solid if you were using tap water as coolant.

You will need to replace that unit.

The heater pipes also keep the throttle at constant temperature to prevent the throttle from prematurely wearing out, its to do with pressure differential causing heat loss (throttle body bore getting cold) which can cause shrinkage of the unit and wear it out.